1. Field of the Invention
This disclosure relates generally to systems, methods, and devices useful for monitoring produced waters coming from, for example, hydrocarbon production processes. More specifically, the disclosure relates to an on-line unit for measuring and optimizing the quality of water after its use in hydrocarbon recovery or production processes, such as a hydraulic fracturing process.
2. Description of the Related Art
Oil and natural gas from shale formations play important roles in meeting the energy demands of the United States. Development of tight oil in the past few years has allowed domestic production of crude oil to increase from 5.1 million barrels a day in 2007 to 5.5 million barrels a day in 2010, reversing a decline in production that began in 1986. Continued development of tight oil will enable the US to produce 6.7 million barrels a day by 2020. Shale gas production is expected to increase from 5 trillion cubic feet in 2010 (23% of total US gas production) to 13.6 trillion cubic feet in 2035 (49% of total US gas production). To enable this large growth in oil and gas supply, numerous new wells will need to be drilled and stimulated via hydraulic fracturing.
Hydraulic fracturing involves pumping a water-sand-chemical mixture into a well at high pressure to fracture the shale formation surrounding the well and allow the natural gas to flow to the wellbore. The water quantities needed for well stimulation can range from 2 to 5 million gallons per well.
When a well begins producing, some of the water used during the stimulation begins to return to the surface. The first three months of production is called the flowback time, and is when the most water is returned to the surface with the oil and gas. After the flowback period, the flow of water returning to the surface slows, but continues. Over the life of the well, the amount of water that returns to the surface can range from as little as 10% to over 70% of the water used for the stimulation, or between 200,000 to 3.5 million gallons of water.
Flowback and produced waters present a challenge to oil and gas suppliers. The water is a resource that can be utilized for further fracturing, but the high levels of total dissolved solids and other contaminants necessitate some treatment or blending of the water before the water can be reused. Treatment of the water can range from simply addition of a biocide such as peracetic acid, to full blown clarification at a water treatment plant. The treatment method is based off of the water quality and desired end use for the water. Blending of produced waters with fresh water can lead to problems if the waters contain incompatible ions such as barium and sulfate, which can lead to scale formation. End water quality must also be considered when blending fresh and produced waters. An on-line water quality monitor would help with the treatment decisions for the water, and also with blending off of the produced water with compatible fresh water.